1. Field of the Invention
The present invention relates to an IC circuit, and more particularly, to an IC circuit capable of generating an internal reference current and showing the state of an IC through one RT terminal.
2. Description of the Related Art
In recent times, the most important element of various electronic devices is power efficiency. A high efficiency switching mode power supply (SMPS) is mainly used as a power supply terminal to constitute an electronic device with high power efficiency. Many ICs for implementing an SMPS are released, and ICs with integrated functions have been released to reduce manufacturing costs. The most efficient method of reducing manufacturing costs is to implement multiple functions through one pin, and the present invention relates to a technology that integrates a function of supplying an accurate reference current and a data communication function of informing the operation state of systems such as IC or SMPS.
First, a method of generating an internal reference current in a typical IC will be described. FIG. 3 shows a typical current source generator. A reference current Iref used inside an IC can be changed through a resistor 1 R1 connected to an RT pin 10. A negative feedback loop, which consists of an amplifier 14 A1, a transistor 13 M3, and the resistor 1 R1, sets a voltage of the RT pin 10 to be equal to a preset reference voltage Vref, and a current Ich of Vref/R1 flows in the external resistor 1 R1. At this time, the generated Ich current generates the internal reference voltage Iref by a current mirror consisting of transistors 11 and 12 M1 and M2. At this time, the generated Iref current varies according to a size ratio of the mirror transistors 11 and 12 M1 and M2.
Next, a method of showing an IC state in a typical IC will be described. FIG. 4 shows an example of configuration of a pin for informing the state of an IC or a system connected to the IC. FIG. 4 is implemented through a transistor 16 M4 inside the IC and a resistor 2 R2 connected between a power voltage VCC and a state information pin 15 STATE in order to inform the state of the IC or the system. If a driving signal (P of the transistor 16 M4 is high, the transistor 16 M4 is turned on so that a voltage of the state information pin 15 STATE becomes almost 0V. When the driving signal (P is low, the transistor 16 M4 is turned off so that the state information pin 15 STATE has the power voltage VCC. Accordingly, it is possible to inform the state of the IC or the system according to the voltage of the state information pin 15 STATE, and this information can be received by another block connected before or after the IC.
In the prior art, as in FIG. 3, a pin for generating an internal reference current and a pin for informing the state of an IC or a system are separately used. That is, in the prior art, an IC with two independent pins is implemented to use both of the above two functions.